A new estimation method for signal frequencies and directions with array antennas

Simultaneous estimation of the centre frequency and the direction of arrival (DOA) of multiple narrow band sources, which may have different centre frequencies, has received considerable attention in the area of array antennas for communication. Many researchers have worked in this area and several methods have been proposed. Previously, we developed a method which computes joint estimations of frequency and direction directly using three non-parallel subarrays. Based on rotational-invariance techniques and with parallel processing, the centre frequencies and the directions of arrival may be computed at the same time as that of one-dimensional TLS-ESPRIT, requiring neither searching in the frequency-direction two-dimensional space nor processing in two stages. However, due to the three subarrays, the array structure will be complex and more antenna sensors (3/spl times/M) will be involved. In this paper we present a modified method for estimation of frequencies and directions based on bi-rotational subspace transformation. Its main advantage over the previous work is that the array is only composed of M antenna sensors and refrains from adopting a complex array configuration. With subspace rotational transformation, we obtain two new signal subspaces and provide the basis of estimation for frequencies and directions of arrival.